They will honor what has been ticketed. But if you call in and make changes to the routings, you will have a problem. As in the case of my wife, who was booked an illegal itinerary, the supervisor said she could only change the flight dates/times but not the routing. Because if she changed the routing, the whole ticket would need to be re-validated and she would lose her initial invalid flights. So in your case, if you want to change the return to get J seats, they might decline your request because your outbound YYZ-NRT-AKL is invalid. But YMMV, you might get lucky with an appropriately ignorant agent.